Control apparatus



May 15, 1951 G. E. UNDY 2,553,019

CONTROL APPARATUS Filed June 16, 1942 2 Sheets-Sheet l ll C179 v 17/0 a i7 2 4 are IN VENTOR 6? 2161 17 H1 j; /zml ATTORNEYS:

May 15, 1951 UNDY 2,553,019

CONTROL APPARATUS Filed June 16, 1942 {Sheets-Sheet 2 /6 7 1 if 3.. E.

CRI

I 0 0 CR a O 0 mm CRSbF-T INVENTOR 5/ B 6 l6Z -4Zl Z yfl iy.

ATTORNEYS- Patented May 15, 195i mesneassignments; to Welt'ronic Company, Oakland. County, Mich, acorporationof; M10111;

gan:

Application June 16', 1942. Serial 1%.447305 The=present invention-- relates to electrical control'apparatus, and in particular providesan improvedresistance welding control system of the ccndens-er discharge type:

The principal: objects of the present-invention are-toprovide-a system-for transferring energyfrom a-source-of power to a work circuit; of the type wherein energy isdeli-vered from-thesource to-energy storageapparatus -at a relatively low rate and is thereafter del'ivered ata relativel y higher 'rate from i thestorage apparatus to the load circuit, which-system is simple-in arrangement and is economicaland eiiicie'nt inoperation; to providesuch=a=system wherein-the euergystorage apparatus-comprises one or more condensers and: :wherein the energy-storedin the condensers is delivered to aresistance-welding load circuit through a-single phase transformer; toprovide such a system wherein successive impulses. are. passed. through i the transformer in alternately opposite: directions; to provide such a system whereinthe reactive-energy storedin theload circuit duringthe courseof one. welding operation. isasreturned to the current storage apparatus so as .to partially. recharge. the same-in readiness for.the next .operation; to provide such a system wherein .the energy. storage apparatus is chargedto; alternately opposite polarities in preparation for. successive welding operations ciated with one. operation serves to -.partia1ly. re-

chargethe storage apparatus. to the. opposite 110-.

larity in preparationfor; the. next operation; to provide. such asystem wherein the energy S1191.- age. apparatus is disconnected from, the, power source prior to the making of each' weldingopr eration and is reversely reconnected thereto at the end of such operation; to provide such an arrangement embodying an improved voltage: regulating system for insuring that thecurrent storage apparatus is charged to the proper dee gree before a welding operation is. initiated; to provide such' an arrangement'emb'odying an improved sequence control'system for determining the successive'work engaging; current flow and related steps of a complete welding operation; and to generally improve the operation and arrangement of control systems of the above indicated type.

With the above as well as other objects in view; which. appear in the following description and in; the. appended claims, a preferred but illustrativeembo dimentof the-invention is shown in the accompanying drawings, throughout the severalviews of which corresponding reference 7 Claims. (01.: 32 -1) characters are used to designate corresponding. parts and which drawings, together, dis'closesaid.

embodiment of. the invention. In thedrawings: Figure 1 is adiagrammatic view of certainof the circuits embodying the invention;

Fig. 2 is a diagrammatic view of the remaining. circuits;

Fig. 3 is a diagrammatic view ofalatrihing type relay; and

Fig. 4 isaviewshowing the. mechanical con-. nection between the various relay coils and the contacts operated thereby.

It will be appreciated from .a complete under.- standing of the invention that certain-oi the fetxturesthereof. may be utilized .indepenedentlyof .others .of the featuresthereof'and that the system as a whole may be. utilized fora Wide variety of purposes other than the herein-specifically descrihed purpose. Apref'erreduse of-the invention is in connection with resistance weld; ing-ap'paratus, adapted to the weld-ingof-certain ofthe relatively low resistance metals (alumi; num, etc.), which require welding current impulses of'relatively high intensity but of' relatively short-duration;

Referring" to the drawings, the illustrativeelec trodes H1 and I2 are connected directlyin the second iy circuit of a usualwelding transformer WT; Current flow throughtheprimary winding of the Welding transformer is controlledloy a pair of reversely connected main rectifiers R1 and R12 which, as shown, are directlyinterpose'd in the primary. circuit of thetransforn er. Rec tifiers Rl ,l and RIZ may be of anysuitabletype, but are preferably of the mercurypoqll y such as, thosesold under the trade namaflgnitron. Rectifiers of this sort will he .understoodasbeing normally non' c'ondu'ctive, but as. beingcapable of being rendered conductiveby applying an igname, potential between the igniter electrodei and the cathode; c atatime when-the anodeajs positive relative to thecathode. When so 116p dered conductive, the rectif ers remain conductiveuntil the current therethrough falls to .SuQh a. low value as to be incapableof maintaining. a discharge through the rectifier, even, though, during suchi current flow, the anode-cathode polarity is reversed. Y

The; main rectifiersR-H and R12 are provided with mean-s comprising electric valves Rl-3- and R114 for selectively rendering the main rectifiers conductive. Valves Rl?3:and.R14, which are preferably of the discontinuous type, are normally non-conductive but are adaptedto be rendered conductive during the course of successive welding operations, as described below.

The main rectifiers RII and RI2 are directly connected to receive energy from one or more condensers CI and C2, which condensers are normally maintained in a discharged condition, when the system is inactive, by means of a discharge circuit including resistor I4 and the normally closed contact CRIIla of a control relay CRIIJ.

The main condensers CI and C2 are disposed to be connected, through the contacts RRa through RRd of a reversing switch, to receive power from a supply transformer ST. The primary winding of the supply transformer is shown as connected in delta and is disposed to receive power from a usual three-phase alternating current source. The secondary windings f the supply transformer ST are shown as connected in star, and as connected to the condensers CI and C2 through a series of rectifiers RI through Rectifiers RI and R4 are associated with one leg of the transformer winding, rectifiers R2 and R are associated with a second leg, and rectifiers R3, R 3 and R1 are associated with the third leg. It is noted that rectifier R'l serves as a trickle charge tube and functions to maintain the main condensers CI and C2 in a, fully charged condition except under conditions when the systern is inactive, or during the course of a welding operation. The rectifiers RI, R2 and R3 are continuously conductive, but rectifiers R4, R5 and R5 are subject to control by a blocking transformer T2, the secondary winding whereof is coupled between the grids and cathodes of rectifiers R4 through R6, through an auxiliary rectifier R8. Transformer T2 is under the control of a voltage regulating relay CR9, the energized or de-energized condition whereof is determined by the degree to which the main condensers are charged. More particularly, the voltage regulating valve R9 functions through transform-er T2 to interrupt the flow of charging current through the rectifiers R4, R5 and R6, when the charge on the condensers reaches substantially the full desired value. voltage the trickle charge tube is rendered nonconductive. Rectifiers RI through R! and R9 may be and preferably are of the usual gas-filled, discontinuous type, and auxiliary rectifiers R8 and RIB, which are associated therewith, may be of any conventional type.

The sequence control system comprises a series of control relays CRI, CR2, CR3, CR4, CR5, CR8, CR1, CR8, CR9, CRIB and CRI I, a latching relay LCR, a short circuiting switch SS and the previously mentioned reversing switch RR, which relays and switches serve, as described below, to control the steps of each individual welding operation, as well as to control the conditioning of the system for the next successive welding operation. Certain of the just-mentioned relays are under the control of a series Of electric valves, designated VI, V2 and V3, which may be and preferably are of the high vacuum continuous control type. switches, with the exception of the relay designated LCR, are of the usual electromagnetically operated type, comprising an operating coil and one or more contacts which bear the same reference characters as the corresponding coil, plus the subscripts a, b, etc. Except as to relay LCR, the several relay and switch contacts occupy the illustrated positions when the corresponding coils are de-energized, but move to and remain in the At a slightly higher value of condenser The just-identified relays and opposite position so long as the corresponding coils are energized.

Referring to Fig. 3, the relay LCR may be of a usual construction disposed to stably occupy either of two positions so long as its coil is deenergized. If the coil is energized, this relay moves to the opposite position, in which it remains until the coil is de-energized and is thereafter re-energized. The relay LCR is provided with a single contact LCRa, which occupies either the open or the closed position, depending upon which of the two stable positions the relay is in. As shown in the drawings, the relay LCR is in such a position that the contact LCRa is open.

The cooperating elements of the contact LCI-ta are carried on arms ll and &9, which are sup ported in an insulating block 5 I Arms and #39 are resilient and tend toward a position in which the contact LCRa is closed. The relay is provided with an armature 35, biased to the position shown by a spring 33, which carries a finger 3'5. Finger 3"? is biased to the position shown by a spring 3%, and cooperates with the successive teeth of a ratchet wheel 4 I, retrograde movement whereof is restrained by a spring pawl =15. The ratchet ii carries a triangular earn it? which in the position shown, and in positions displaced 128 therefrom, engages arm 41 and holds the contact LCRa in the open position. In the intermediate three positions, the cam H allows the contact to close. As will be obvious, each energization of the coil enables finger 37 to advance the ratchet one step. When the coil is de-energized, spring 39 yields and allows the finger to move downwardly and clear the ratchet during the return movement of the armature as influenced by spring 33.

It is thought that the remaining details of the system, including a description of the specific functions performed by the elements thereof, may best be understood from a description of the operation of the system as a whole.

The system may be conditioned for operation by closing the disconnect switch, designed LS at the top of Fig. l, which action immediately energizes the supply transformer ST and also immediately energizes the control transformer CT. Upon being energized, the control transformer CT supplies alternating current to the control conductors, designated i8 and I3 in Fig. 1, and correspondingly designated in Fig. 2. In addition, the energization of the control transformer may be and preferably is arranged to supply energizing current to the primary windings of all of the transformers which are designated a: in Fig. l, which transformers, as will be understood, serve to supply filament current for rectifiers RI through RIB, and to also supply filament current to valves VI, V2, and V3 of Fig. 2.

In Fig. 1, the energization of line conductors I5 and I8 completes energizing circuits for the primary windings associated with transformers TI, T3, T6, and TV. If desired, a voltage regulating unit CV may be interposed between the source Int-Iii and transformer T3 so as to render the output of transformer T3 uniform and free of fiuctuatious of the voltage of the source. Transformers TE and T7, respectively, are coupled to the grids of the firing valves RI3 and RI 4 through rectifiers R! 5 and RI 6, and upon being energized, become effective to apply negative biases to these grids, thereby rendering valves RI 3 and RM nonconductive.

Transformer T3 is connected, through rectifier 5.? R l 0, across resistor 2 ll} and; upon beingenergized; is effective to impress apotential acrosstthis re? sistor having the polarity indicated in the draw ing. Resistoris coupled between the grid and cathodeofrectifier R9 through the potentiometer resistor- 22 and conductors-24 26, 28,311; 21 and 25. Under the conditions-stated, the main condensers Cl-C2-' are discharged, and are not effective to impress a potential acrossresistor:22.

The just-mentioned'potential of resistor 20, accordingly,bringsthe-grid of Valve R9 to a positive value relative to the cathode-'of' thislvalve and renders the valve conductive. r Similarly, .resistor 20 iscoupledbetween thegrid and cathode of the trickle charge valve R'l through' conductors 24, 2B, 32, 29 and- 25, andthejust mentioned potential, therefore, serves to'render thes-trickle charge valve conductive.

Upon being: energized, transformer Tl applies anode potential to the now conductive rectifier R3; which action energizes: control: relay- CR9 andcauses the normally closed back contact .CRSa of this relay to open. This action interrupts an otherwise complete energizing'circuit for theprimary winding of control transformer T2; associated with rectifier R8. -As: aforesaid, transformer T2 is coupled, through the rectifier- R8, between the vgrids and cathodes of valves R4 through R6 and when energized, serves to apply a negativeor blocking bias -to the grids of these valves-which renders themnon-conductive. The de-energization of transformer T2 removes this blocking bias and brings valves R4 through R6 to a conductive condition. 1

The energization of line conductors Hiand l8 also completes an obvious energizing circuit'in Fig. 1 for the coil of control relay CRIB, which thereupon opens'its sole contact CRHIa and-interrupts the previously mentioned normally complete discharge circuit forcondensers ClahdCZ.

Before describin the charging of the main condensers Cl and 02, which results from the unblocking of rectifiers' R4 through R1; attention is invited to the operations which result in Fig. 2 from theenergization of line conductors It and 18. The energization of these conductors in Fig. 2 completes obvious energizing circuits for the primary windingsof transformers TiZ', Ti5 and Tit, which are associated,respectively, with the; grid circuits of control valves'Vl, V2 andV3. Upon being energized, these-transformers apply blocking biases tothe grids of the. cor)- responding valves, andalso supply charging cur; rent to the associated grid condensers 03,04, C5 and'C6,.'which actions render the corresponding valves. non-conductive; in preparationfora weld-'- ing operation.

The energization of the supply transformer ST, coupled with the unblocking' of rectifiers. R4 through Rl, enables the supply transformer ST to pass current throughrectifiers RI thrioughR'l (rectifier-s RI, R2 and R3 being continuously corrductive) to thepositive bus 26 and thecorresponding negative bus 34. Under the. conditions stated, contacts RBI) and RRc or" thereversing relay RR are closed, and contacts RRct andjRRd thereof areopen. Consequently; bus 26 is con-- nected' to bus. 36,.and' bus 34 is connected to bus 38, and the flowof current from the supply transformer ST thus charges condensersCl "and C2 "in such a" direction that: the P13118810, thereof arepositive.

As the condensers charge up, .thellp'otentialof the point 49 on .thepotentiometer'22,"at which the adjustabletap is set; becomes" progressively sweaters 6. more- -negative withrespect. to theapotential ofithe bus 26. When a predetermined condenseripotentia-l is attained, corresponding. to substantially;av

fier R9 is rendered non-conductive. Upon b'eing non-conductive, rectifier RQade-energizes control relay CR9; which thereupon recloses. its; contact CRBain Eig. landxalso recloses itscOntactGRSb in- Fig. 2. The latter action conditions thel se quencecircuits,.as:described below, for a welding operation sand the former actionre-energ-izes transformer T2. Upon being so re-energized, transiormer T20 applies a blocking biastothe grids of rectifiers R4,- R5 andn-Rii, interrupting further charging. action through. these rectifier-s; Thechargingaction; however, continues through thetrickle. charge valve R1 andjrectifiers- -Rl and R2 At a. slightly higher condenser potential, the potential. of the: point 4d reaches apsufiiciently negative. value to block-thetrickle charge valve R1, it being understood that valves R7 and RS have slightly diiferent characteristics and; consequently, become blocked at; slightly different critical potentials. of their grids relative to their cathodes. The blocking. of the trickle charge valve. entirely interrupts further charging-action. If the. system remains idle for a sufiiciently long period to allow the charge on-the main con+ densers Cl .and C2 to leak off to an appreciable degree, the rise in potential of the point 40,- relative. to the bus 26; unblocks the trickle charge Valve R1 and enables the rsupply transformeroto restore-the condensers to the fullycharged condition.

Referring now to Fig. 2, the: illustrated-sequence control system'is providedwith two pilots or starting switches, designated Pl andPL The pilot switchPi serves to actuate the mechanism which bringsrthe electrodes into clamping. engagement withthe work,'and"the pilot switch P2 serves to initiate the flow of welding-current and other steps which are incidental to a welding operation. Pilot switches Pi and P2 may-be arranged foreither manual or automatic operation, but :are illustrated as being-manually operable. Assuming it is desired to effect a Welding operation, the pilot switch Pl may be closed, which. action completes an obvious circuit for the 'pri-- mary winding of transformer T8, whichcircuit; alsoincludes a normally closed clear-out-switch 5d. Uponbeing energized, transformer T8 ener-. gizes control. relay-CRi through the normally conductive valve VI; Upon being energized-,-c'on trol relay CRl closes its normally open contacts CRiaaand CRib. Closure of these contacts completes, a circuit for the solenoid 52; also desige nated valve, which solenoid, as willbeunderstood, maybe associated with usual fluid pressure operated means,- which upon being actuated move the electrodes into clamping engagement with the work.- It ,willbe noticed that this action may be accomplished independently of the charged or uncharged condition of the main condensers Cl and, 02. If, the pilot switch PI is released, the just-mentioned circuits are interrupted resulting in the separation of the electrodes" from the work.

In making a weld, however, the pilot'switch 'Pi is maintained closed until after the closure of the'companion pilotswitch P2", which latter pilot switchmay be closed eitherb'efore," simultane-fv 7 ous ly with, or after the closure of pilot switch Pl.

Provided relay CRI has been energized by closure of pilot switch Pl, closure of pilot switch P2 completes an obvious energizing circuit for the coil of relay CR2, and for the primary winding of transformer Tl I and, subject to the previous closure of contact CRSb, also completes a circuit for transformer T l i].

Upon being energized, relay CR2 closes its contacts CRZa, CRZb and CRZc. Contact CR2a completes a holding circuit in parallel with the pilot switch Pl, which may thereupon be released to the open position without effect upon the welding cycle now in progress. Contact CRZZ) completes a self-holding circuit for relay CR2, enabling pilot switch P2 to also be released to the open position without effect upon the cycle now in progress. Closure of contact CR2c com-' pletes a circuit for relay CR1, which thereupon closes its contact CRM and energizes the short circuiting switch SS. Upon being so energized, the short circuiting switch SS opens its sole contact SSa, removing the short circuit from the secondary winding of the welding transformer WT in Fig. 1.

Upon being energized, transformer Tl l opposes the normally energized transformer T|2 and enables the energy previously stored in the grid condenser C4, associated with valve V2, to start discharging through the associated resistor At the expiration of a relatively short period determined by the characteristics of this discharge circuit, the grid of valve V2 assumes a value at which this valve is conductive. It will be under stood that this delay period is calculated to be long enough to insure that the electrodes are in clamping engagement with the work before the flow of welding current is initiated. From the previous description of Fig. 1, it will be appreoiated that contact CRSb reclosed when the main condensers Ci and C2 reached a fully charged condition, so that the previous closure of pilot switch P2 was effective to energize transformer TIO, associated with the anode circuit of valve V2. curred during the charging period of the main condensers, all of the aforesaid actions attributed to the closure of pilot switches Pi and P2 would have occurred with the exception that the energization of transformer Till, which serves to actually initiate the fiow of welding current, would have been delayed until after the reclosure of contact CR9b.

Upon being energized, transformer Tlfi applies anode potential to valve V2 and, assumin valve V2 is conductive, as aforesaid, this action completes an energizing circuit for relay CR3, which thereupon closes its contact CR3a (Fig. l) and also closes its contacts CR3b and CR3c in Fig. 2. Closure of contacts CR3a completes a maintaining circuit for transformer T2, which maintains this transformer energized until the expiration of the welding cycle now in progress and, consequently, maintains charging rectifiers R4, R5 and R6 in a blocked condition. Closure of contact CR3b completes a circuit in parallel with the now closed contact CRBb, and serves to maintain transformer TIB energized until the expiration of the welding cycle now in progress.

Closure of contact CR3c completes energizing circuits for the coils of relays CR5 and CRI I, and for the primary windings of transformers T13 and TM, associated with the anode and grid circuits of valve V3. Upon being energized,

If the closure of the pilot switches had ocrelay CRH opens its sole contact CRHa and disconnects the trickle charge rectifier R! from the supply transformer, thus preventing flow of current through this rectifier until after the expiration of the welding cycle now in progress. Upon being energized, relay CR5 closes its contact CRM in Fig. l. and completes an energizing circuit for the firing transformer T4, associated with firing valve R13. This circuit includes the now closed contact CRGa of the control relay CR8, which is synchronized with the reversing switch RR and serves to determine which of the main rectifiers RH and Rl2 is to be fired in accordance with the polarity to which the main condensers Ci and C2 are charged. Upon being energized, transformer T4 applies a potential between the grid and cathode of firing valve Rl3, which overcomes the negative M- as of transformer T8 and renders valve R13 conductive. As will be noted, the anode circuit of firing valve R!3 is connected between the anode and the igniter electrode 2' of rectifier RI 1, and upon being rendered conductive, consequently, is effective to appiy a firing potential between the igniter i and the cathode of rectifier RH which action renders this main rectifier conductive.

Upon being rendered conductive, rectifier RH enables condensers CI and C2 to discharge the energy stored therein through the welding transformer WT, which action causes welding current to flow through the electrodes i0 and I2 and the work. It will be understood that the reactive energy stored in the welding transformer serves to maintain the flow of current through the circuit, including the condensers Cl and C2, the rectifier Rl I, and the welding transformer WT, in the same direction as the impulse of current delivered from the condensers. This continued flow of current dissipates the energy stored in the welding transformer and also partially recharges the main condensers CI and C2 to a polarity opposite to the original polarity; that is, to a polarity such that the plates 22 of condensers Cl and C2 are positive. The thus partially recharged condensers are ineffective to cause a reverse flow of current through the welding transformer, since rectifier RI I will pass current only in the original direction, and since the other rectifier R22 is in a non-conductive condition. The welding current thus flows in a single unidirectional impulse, the form, maximum value and duration of which is, of course, determined by the constants of the circuit, including the welding transformer and power condensers. These latter constants also, of course, determine the proportion of the original charge on the condensers which is returned to them from the welding transformer and the proportion of such energy which is dissipated as heat in the welding circuit.

The reduction in condenser voltage, incident to the discharge action, raises the potential of the potentiometer point 48 relative to the potential of the bus 25, and enables the potential impressed across resistor 29 to bring the grids of rectifiers R1 and R9 to values at which these valves are conductive. The bringing of rectifier R1 to a conductive condition, however, is without effect since contact CR! Id of control relay CRIl is in the open condition, and it is here noted that this contact remains open until towards the close of the re-setting operations which follow the fiow of the welding current. The bringing of rectifier R9 to a conductive condition enables transformer TI to re-energize control relay CR9, which there 9 upon re-opens it contact CRSa. .This action does not interrupt the energizing circuit for transformer T2, however, since the parallel relay contact CRM is in the closed condition. Contacts CRI l a and CRSathus serve to maintain the charging circuits in a blocked "condition until after the flow of the welding current'ha's ceased and the system is in readiness for the recharging operation.

The re-energization of relay CR9 also causes its contact CR9b (Fig. 2) to re-open. This action is, however, without effect since the now closed contact CR3!) of control relay CR3 isconnected in parallel therewith'and serves to maintain the circuit for transformer TH].

Reverting to the sequence diagram, the energization of transformers T43 and TM, whichoccurred simultaneously with the initiation of the condenser discharge, conditions relay CR4 for operation. More particularly, transformer TM opposes the continuously energized transformer Tl5 and enables the energy stored in condenser C5 to discharge through the associated resistor 56. At the expiration of a period determined by the characteristics of this discharge "circuit, the grid of valve V3 assumes a'value at which this valve is conductive. It will he understood that this period, which is adjustable. is proportioned to be slightly in excess of the time required for the full discharge'and the partial recharge of the main condensers. At the expiration of this timing period, transformerTl-B is enabled to pass current through the nowconductive valve V3 and energize control relay CR4.

Uponbeing energized, relay CR4 closes contact CR4!) and opens contacts CR la and-CRdc. The opening of contact CR la interrupts the previously traced-energizing circuit for the coil of relay CR5, which thereupon resumes the dc-energized position. This action opens contact CR5a and interrupts the circuit for the firing transformer T4 (Fig.-1),-enabling transformer T6 to again apply a blocking bias to the grid of valve R13. It will be understood that rectifier RH became non-conductive at the expiration of the flow of recharging current to the main condensers, so that-rectifier RH and its associated firing valve RI3 are now restored to their original non-conductive conditions.

The opening of contact CR lc interrupts the previously traced energizing circuit for the coil of relay CR1, which thereupon resumes the deenergized position, and opens its contact CRla. The opening of this contact interrupts the circuit for the short circuiting switch, which thereupon recloses its contact 8312 in parallel with the secondary winding of. the welding transformer. This action insures the fully de-energizing condition of the welding transformer, preparatory to the separation of the electrodes l0 and E2.

The closure of contact CR4b completes an energizing circuit for transformers Tl-fiand TI! associated with the anode and grid circuits of valve V4. Upon being energized, transformer Til opposes the continuously energized transformer TH and enablesthe energy stored in condenser C6 to discharge through the associated resistor 58. At the expiration of a timing pe riod determined by the characteristics of this discharge circuit, valve V4 is rendered conductive and enables the 'now energized transformer TIE to energize control relay .CRfi. It will understood that this timing period, usually called a hold-tirne period, is proportioned to enable the weld to set after the flow of welding current 10 has ceased and before the electrodes ti! and l2 are separated.

Upon being energized, at'the expiration of this hold-time period, relay CR6 serves to resetthe sequence circuits in preparation for the next welding operation-and also conditions the power circuits to effect the-completion of the recharging of the power condensers. More particularly, relay CR6 closes its contact CRfiband completes a circuit for the coil 'of the latching relay LCR. This action throws relay LCR to its opposite position, in whichits contact LCRa is closed, and it will be recalled that this relay remains in this opposite position, after being so moved, until its coil is de-energized and is again energized. This re-energization-of the coil of the relay LCR does not take-place until the correspond-ing stage of the next successive welding operation is reached.

Closure of contact LCRa completes parallel energizing circuits for the windings of the reversing switch RR and the control-relay which windings, consequently, remain energized .until the above-mentioned stage of the next welding operation. With its coil-RR energized, the reversing switch moves-its contacts RRa and RRcZ to the closed position and opens its contactsRR-b and RRc. As is -obvious fronrFig. 1, this action disconnects buses 25 and 34 from buses 36 and .38, respectively, and connects them to buses-38 andBE, respectively, thereby conditioning the power condensers CI andC-Z to re ceive charging current from the supply transformer in such a direction as to bring the condenser plates b to the positive polarity. Upon being energized, control relayCRB 'opens its contact CR8a in Fig. l and closes its contact CRtb. Thisaction prevents the closure of control relay contact CRSa (duringthe next welding operation) from energizing firing transformer T4, but enables-such action to energize firing transformer T5 associated with the other main rectifier Rl2.

Upon being energized,- relay CR6 also closes-its contact CRiia and energizes grid transformer T5, associated with valve VI. Upon being energized, transformer Til-applies a blocking bias to the grid of valve VI, thereby preventing further flow 9f current through this valve, and also charges up the olf-time condenser C3, which functions, as hereinafter described, to prevent the re-initiation of a subsequent welding operation until after the expiration of a predetermined off period during which the work may be appropriately moved relative to the electrodes in preparation for such next welding operation.

When valve V! is blocked, control relay CRI resumes the de-energized position, opening its contacts CRM. and CR). This action de-energizes the valve solenoid 52, enabling the separation of the electrodes from the work, and also de-energizes relay CR2. Upon being de-energized, relay CR2 interrupts the circuit for transformers T16 and TH, which action restores the circuits associated with valve V2 to their original condition and also results in the de-energization of relay CR3.

Upon being de-energized, relay CR3 re-opens its contacts CR3a, CR3b and CR3c. The re-opening of contact CR3a interrupts the circuit for. transformer T2, since, as aforesaid, contact CRBa is now open. The consequent de-energizationof transformer T2 removes the blocking bias from the grids of the charging rectifiers as, R5 and Rt, and enables the supply transformer ST to initiate a recharging of the condensers C'l 11 and C2 through rectifiers RI through R6, the recharging action in this case being in a direction to bring the plates 19 of condensers CI and C2 to the positive polarity.

The re-opening of contact CR3b is without immediate efiect, since the circuit for transformer TH] is now interrupted at contacts CRla and CRZb. This re-opening, however, does render the circuit for transformer TII] subject to the condenser-voltage-responsive relay contact CRSb, thus preventing the re-initiation of a new welding cycle unless and until the power condensers reach a fully charged condition.

The re-opening of contact CR3e interrupts the circuits for control relay CRII and for transformers TI3 and TM. The de-energization of control relay CRII causes its sole contact CRI ia to reclose in Fig. 1, which action reconnects the trickle charge rectifier Rl to the supply transformer ST and again renders this rectifier effective to cooperate in maintaining the condensers CI and C2 in a fully charged condition.

The de-energization of transformers TI3 and TI4 restores the circuits associated with valve V3 to their original condition, and also deenergizes control relay CR4, which thereupon opens its contact CR4?) and recloses its contacts CRM and CR Ic. The reclosure of contacts CR4a and CR4c is without immediate effect (since the associated circuits are elsewhere interrupted), but prepares the system for the next operation. The re-opening of contact CR Ib interrupts the circuits for transformers TIE and TIT, which restores the circuits associated with valve V4 to their original condition and de-energizes control relay CR6. This latter action causes contacts CHM and CR6b to open. The latter action serves to de-energize the coil of the latching relay LCR, which action is without immediate effect, since, as aforesaid, this relay is stable in either of its two limit positions. The former action interrupts the energizing circuit for transformer T9 and enables the energy stored in grid condenser C3 to start discharging through the associated resistor 60. At the expiration of a predetermined offtime, determined by the characteristics of this discharge circuit, the grid of valve VI assumes a value at which this valve is conductive, and if at the end of this period pilot switch PI is still closed, or is reclosed, a new welding cycle may be initiated, as aforesaid.

The foregoing resetting operations restore the sequence and power circuits of Figs. 1 and 2 to their original condition, with the exception that relay LCR is now in its opposite position. and that, consequently, the reversing switch RR and the control relay CR8 are in their energized conditions. As aforesaid, these differences serve to reverse the connections between the buses 25 and 34 and buses 35 and 38, and to provide that the next welding operation will result in the firing of rectifier RI2, instead of rectifier RII. The completion of the recharging of the power condensers CI and G2. which was re-initiated when the charging rectifiers R4, R and R6 were rendered conductive, serves, as before, to bring the condensers to a fully charged condition, at which time these rectifiers are again blocked in the previously described manner, leaving the trickle charge rectifier R1 effective to maintain the condensers in the fully charged condition.

If a new welding cycle is initiated at the 6X- piration of the above-mentioned off-time, as determined by the oif-time condenser C3, the en tire sequence is as described above with. the ex ception that in this case the energization of control relay CR5 energizes transformer T5, which thereupon fires rectifier RM and causes the firing of rectifier RIZ, instead of energizing transformer T4 and causing the firing of rectifiers RI3 and RI I. In this case, the consequent firing of rectifier RIZ enables condensers CI and C2 to discharge through the welding transformer WT, the current flow being in a direction opposite to that described in the first instance. In this case, also, the partial recharging of the condensers CI and C2 takes place through rectifier BIZ and again brings the condensers to a charged condition in which the plates (1 thereof are positive. During the resetting operations which follow the welding cycle now being described, also, the closure of relay contact CRBb energizes relay LCR, which thereupon moves to its opposite position and re-opens its contact LCRa. This action de-energizes the reversing switch RR and the control relay CR8, restoring the contacts of these members to the positions shown in Fig. 1. These actions, as will be understood, connect the condensers to the power source for recharging in the original direction and also condition the circuits associated with rectifiers RH and RH! to effect the next firing action through rectifier RI I.

It will be observed that so long as the pilot switches PI and P2 are maintained in the closed position, the system will go through successive welding cycles and intervening off-times, as described above, and that, further, the pilot switches PI and P2 may be opened during the course of any such welding period without affect ing the same and without altering the off-time, which must intervene between successive welding cycles. In certain cases, it is desirable to enable the operator to delay or postpone certain of the resetting operations which normally follow the cessation of the flow of welding cur rent. In the present system, this may be accomplished by moving the manually controlled throw-over switch 62 from the illustrated righthand position to the illustrated lefthand position. If this is done, the operator, by maintaining the pilot switch P2 in the closed position, can free the circuit for relay CR2 from control by relay CRI. With switch 62 in the lefthand position, the operations involved in initiating and causing a flow of welding current to the welding circuit are as previously described. When relay CR6 is energized at the close of the hold-time period which follows the welding period, it closes contact CRBa and blocks valve VI, as before. As before, also, relay CRI thereupon resumes the de energized condition and de-energizes the valve solenoid 52. This action, as before, results in the separation of the electrodes I 0 and I2 and the release of the work. If the pilot switch P2 has been released to the open position, the de-energization of relay CRI also causes all of the other resetting operations, which are described above, and which are initiated by the consequent de-energization of relay CR2. If, on the other hand, in the sequence now being described, pilot switch P2 is maintained in the closed position, the de-energization of relay CRI is ineffective to de-energize relay CR2 and, consequently, the only resetting operation which follows the flow of weldin current is the separation of the electrodes and the release of the work. So long as the operator maintains the pilot switch P2 in the closed position, the other resetting operations, including the recharging of the condensers CI and C2, are held 13 in abeyance. ,As soon, however, as the operator re-opens pilot switch these resetting and recharging operations go forwardas before.

It will be noticed that certain/50f I, the circuits in Fig. 2 extend through theclear-out switch 50. This switch normally occupies the closed position. By moving this switch to the open position,- however, a, convenient means is afforded for-preventing actuation of the sequence control circuits, eventhough pilot switches PI and P2 are closed, thus enabling the operator to perform necessary inspection, maintenance,- or other operations upon the machine without'makingit necessary to open-the main disconnect switch LS, which action would, of course, also involve discharging the condensers.

Although only a single Specific embodiment of the invention has been described in detail, it will be appreciated that various modifications inthe form,- number and arrangement of parts may be made without departing from the invention.

What is claimed is:

1. In a system for supplying pulses of current from a source of alternating current to a reactive load circuit, the combination of energy storage means, means including selectively controllable means and rectifying means interposed between said source and said storage mean for delivering charging current to said storage means in either of two directions so as to charge said storage means to either of two polarities, control. means including asymmetric conducting means interposed between said storage means and said load circuit and normally effective to prevent flow therebetween of a said pulse, means operable to render said charging means ineffective to deliver charging current to said storage means and to render said control means effective to pass a said pulse of current between said storage means and said load circuit during which the storage means supplies energy to the load circuit and the load circuit returns energy to and recharges the storage means to a polarity opposite to the original polarity thereof, means controlling said charging means for increasing the charge on said storage means in said opposite polarity, and means for controlling the operation of said operable means in accordance with the charged condition of said storage means.

2. In a system for supplying pulses of current from a source of alternating current to a reactive load circuit, the combination of energy storage means, means including selectively controllable means and rectifying means interposed between said source and said storage means for delivering charging current to said storage means in either of two directions so as to charge said storage means to either of two polarities, control means including asymmetric conducting means interposed between said storage means and said load circuit and normally effective to prevent flow therebetween of a said pulse, means operable to render said charging means ineffective to deliver charging current to said storage means and to render said control means effective to pass a said pulse of current between said storage means and said load circuit during which the storage means supplies energy to the load circuit and the load circuit returns energy to and recharges the storage means to a polarity opposite to the original polarity thereof, and timing means rendered effective by actuation of said operable means for again rendering said charging means effective to deliver charging current to said storage means in said opposite polarity.

M 1 3-.-'In a system-for supplying pulses of: current from a source of alternating current 110: are active load circuit,- the combination of==energy storage means, means including selectively con trollable means and rectify-ing means interposed between said source and said storage'rneans for delivering charging current tosaid storagemeans in either of two directions so as to charge said storage means to either of two polarities, -said charging means being normallyeffective, sc -long as the potential of said storage mean is below a predetermined value, to effect such deliveryof charging current, control means including asymmetric conducting means interposed between said storage means and said loadcircuit and normally effective to prevent flow therebetween-of a said pulse, means operable solely subsequent to the attainment'of said predetermined potential value .by saidstoragemeans to render saidcharging means ineffective to deliver charging current to said storage means :and to render said'control means effective. to pass a saidv pulse of current betweensaid storageumeans and'said load circuit during which-the storagesmeans supplies energy. tothe load circuit and the load circuit, returns energy to and recharges the storage means to a polarity opposite to the original polarity thereof, and means controlling said charging means to supply additional charge to said storage means in said opposite polarity.

4. In a system for supplying power to a reactive load circuit, the combination of an energy storage device chargeable to either of two opposite polarities, means coupling said device to said circuit so as to enable the device when charged to either of said polarities to supply energy to the circuit and to enable reactive energy stored in the circuit to be returned to and partially recharge the device to the opposite polarity, control means rendered effective as a consequence of said storage device attaining a predetermined charge for actuating said coupling means to effect a said supply and return of energy, and additional means rendered effective as a consequence of an actuation of said control means for coupling said device to a source of power so as to complete the recharging thereof to said opposite polarity.

5. In a system for supplying power to a reactive load circuit, the combination of an energy storage device chargeable to either of two opposite polarities, means coupling said device to a source of power for enabling delivery of charging current thereto in either of two directions, means coupling said device to said load circuit so as to enable the device when charged to either of said polarities to supply energy to the circuit and enable reactive energy stored in the circuit to be returned to and partially recharge the device to the opposite polarity, control means for actuating said last-mentioned coupling means to effect a said supply and return of energy and for preventing delivery of charging current to said device from said source during said flow of energy, and means effective as a consequence of the operation of said control means and solely subsequent to said device having received a predetermined charge for rendering said first-mentioned coupling means effective to complete the recharging of said device to said opposite polarity.

6. In a system for supplying power from a source of periodic current to a reactive load circuit, the combination of an energy storage device chargeable to either of two opposite polarities,

means coupling said device to said source so as to enable said source during the course of a plurality of periods thereof to charge said device to either of said polarities, means coupling said device to said load circuit and controlled by the charge of said storage device to enable the device when charged to one polarity to supply energy to the circuit solely in a one direction whereby the reactive energy stored in the circuit is returned to and partially recharges the device to the opposite polarity, and means effective to control said first-mentioned coupling means so as to complete the charging of said device to said opposite polarity.

7. In a condenser system, a condenser, means for charging said condenser, a circuit for discharging said condenser, means responsive to the charge on said condenser for preventing establishment of said circuit When the charge on said condenser is below a selected level, and a single means for simultaneously and correspondingly adjusting the condenser charging means and said preventing means to select the voltage above which said circuit may be established.

GUSTAV E. UNDY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,168,346 Thomson Jan. 18, 1916 1,781,792 Rodman Nov. 18, 1930 1,980,899 Bedford Nov. 13, 1934 2,106,831 Dawson Feb. 1, 1938 2,179,105 Sidney Nov. 7, 1939 2,250,102 Klemperer July 22, 1941 2,287,540 Vang June 23, 1942 2,295,293 Rogers Sept. 8, 1942 2,502,887 Rava Apr. 4, 1950 FOREIGN PATENTS Number Country Date 548,618 Great Britain Oct. 16, 1942 

